Distinct RopGEFs Successively Drive Polarization and Outgrowth of Root Hairs

First author: Philipp Denninger; Affiliations: Heidelberg University (德国海德堡大学): Heidelberg, Germany

Corresponding author: Guido Grossmann

Root hairs are tubular protrusions (突起) of the root epidermis that significantly enlarge the exploitable soil volume in the rhizosphere. Trichoblasts, the cell type responsible for root hair formation, switch from cell elongation to tip growth through polarization of the growth machinery to a predefined root hair initiation domain (RHID) at the plasma membrane. The emergence of this polar domain resembles the establishment of cell polarity in other eukaryotic systems. Rho-type GTPases of plants (ROPs) are among the first molecular determinants of the RHID, and later play a central role in polar growth. Numerous studies have elucidated mechanisms that position the RHID in the cell or regulate ROP activity. The molecular players that target ROPs to the RHID and initiate outgrowth, however, have not been identified. We dissected the timing of the growth machinery assembly in polarizing hair cells and found that positioning of molecular players and outgrowth are temporally separate processes that are each controlled by specific ROP guanine nucleotide exchange factors (GEFs). A functional analysis of trichoblast-specific GEFs revealed GEF3 to be required for normal ROP polarization and thus efficient root hair emergence, whereas GEF4 predominantly regulates subsequent tip growth. Ectopic expression of GEF3 induced the formation of spatially confined, ROP-recruiting domains in other cell types, demonstrating the role of GEF3 to serve as a membrane landmark during cell polarization.

根毛是根表皮的管状突起，显著扩大了根际的可利用土壤量。生毛细胞，是一类能够形成根毛的细胞，通过生长机制的极性化从细胞伸长转变为尖端生长，预定义质膜上的根毛起始结构域RHID。该极性结构域的形成在其他真核生物中往往代表了细胞极性的建立。植物Rho类GTP酶ROPs是RHID首先的分子决定因素之一，并在之后的极性生长中发挥重要作用。许多研究已经揭示了RHID在细胞中的定位以及ROP活性调控的分子机制。但是到底是什么分子帮助ROP定位到RHID以及起始往外生长还不清楚。作者详细研究了极化根毛细胞的生长机制，结果发现ROP的定位以及往外生长是两个分开的进程，各自都由一个特定的ROP鸟嘌呤核苷酸交换因子GEFs所调控。对于生毛细胞特异性GEF的功能鉴定显示正常的ROP极性化需要GEF3的作用，而GEF4则主要调控后续的根毛尖端生长。GEF3在其他细胞中的异位表达诱导ROP招募结构域的形成，揭示了GEF3在细胞极化过程中作为膜标记发挥功能。

通讯：Guido Grossmann（https://www.cos.uni-heidelberg.de/index.php/g.grossmann?l=_e）

研究方向：质膜中蛋白的横向扩散；细胞壁和细胞骨架对膜组织的影响；细胞极性的建立；响应于信号感知的信号处理。

doi: https://doi.org/10.1016/j.cub.2019.04.059

Journal: Current Biology

Published date: May 16, 2019